This invention relates generally to an improved burner assembly, and more particularly, to an improved fuel burner assembly for heating and drying aggregate materials used in connection with the production of hot mix asphalt.
It is known to use a fuel burner assembly to heat and dry aggregate materials used in connection with the production of hot mix asphalt. See, e.g., U.S. Pat. Nos. 5,700,143; 5,511,970; 4,559,009; and 4,298,337. However, conventional burner assemblies suffer from several disadvantages. For example, conventional burner assemblies are incapable of producing a flame configuration satisfactory for asphalt production in a variety of different-sized combustion chambers. As a result, burner assemblies typically include adjustable spin vanes to accommodate different-sized combustion chambers. For example, U.S. Pat. No. 6,488,496 of Feese et al. describes a compact combination burner with an adjustable spin rack. Adjustable spin vanes, however, increase the cost of manufacture, the likelihood of repair, and the amount of labor required to operate the burner.
In addition, burner assemblies having castellated elements are known and disclosed by U.S. Pat. Nos. 2,840,152 and 1,676,813. These burner assemblies, however, do not utilize the castellated elements to maximum advantage. It would be desirable, therefore, if an apparatus could be provided that could be used to produce a stable flame configuration that has a short flame length and a narrow flame diameter adapted for use on a wide variety of different-sized combustion chambers. It would also be desirable if such an apparatus could be provided that would more completely and evenly mix fuel and air in order to obtain more rapid combustion, thereby reducing the combustion space required in the asphalt drum and lowering carbon monoxide (CO) emissions in the combustion space. It would be further desirable if such an apparatus could be provided that would reduce the temperature of the dryer drum breech plate where the burner is mounted. It would be still further desirable if such an apparatus could be provided that would eliminate the need to adjust spin vanes to achieve a desired flame configuration. It would be still further desirable if such an apparatus could be provided that would achieve reduced nitrous oxide (NOx) emissions. It would also be desirable if such an apparatus could be provided that would be less complicated and expensive to manufacture, operate and maintain.
Accordingly, it is an advantage of the invention claimed herein to provide an apparatus for producing a stable flame configuration that has a short flame length and a narrow flame diameter. It is also an advantage of the invention to provide an apparatus for producing a flame configuration that is adapted for use on a wide variety of different-sized combustion chambers having different-sized combustion spaces. It is another advantage of the invention to provide an apparatus that more rapidly, completely, and evenly mixes fuel and air, thereby improving combustion intensity, reducing the combustion space required in the asphalt drum, and reducing CO emissions in the combustion space. It is still another advantage of the invention to provide an apparatus that reduces the temperature of the dryer drum breech plate. It is yet another advantage of a preferred embodiment of the invention to provide an apparatus that achieves reduced NOx emissions. It is a further advantage of the invention to provide an apparatus that eliminates the need for adjustable spin vanes in order to achieve a desired flame configuration. It is a still further advantage of the invention to provide an apparatus that is less complicated and expensive to manufacture, operate and maintain than conventional burner assemblies.
Additional advantages of the invention will become apparent from an examination of the drawings and the ensuing description.
As used herein, the term castellated ring refers to both an integral, contiguous ring having two effective diameters produced by castellated and non-castellated portions of the ring. In addition, the term castellated ring also refers to a plurality of castellations mounted in a spaced apart relationship to each other around an annular channel, air tube, opening or the like so as to produce two effective diameters in the annular channel, air tube, opening or the like.
As used herein, the terms total open area of the burner end or total open area of the burner end of the housing refer to the cross-sectional area of the burner end of the housing. More particularly, the terms total open area of the burner end or total open area of the burner end of the housing refer to the cross-sectional area defined on its outer perimeter by the housing.
As used herein, the terms low fire or firing on low fire refer to a nominal or minimal burner firing rate. More particularly, the terms low fire or firing on low fire refer to a firing rate of at least one-seventh of the total fuel and air input rate of the burner assembly.
The invention comprises a burner assembly including a housing having an air inlet and a burner end. An impeller that is mounted in the housing is in communication with the air inlet and adapted to direct air toward the burner end of the housing. The burner assembly also includes an inner air tube that is mounted in the burner end of the housing so as to define an inner combustion zone and an outer combustion zone. The assembly further includes a plurality of radiation plates that are mounted in the burner end of the housing adjacent to the outer combustion zone, an inner air spin vane that is mounted on the inner air tube so as to direct some of the air from the impeller into the inner combustion zone, an inner gas injection nozzle mounted on the inner air tube so as to direct gaseous fuel into the inner combustion zone, an outer air spin vane that is mounted in the burner end of the housing so as to direct some of the air from the impeller into the outer combustion zone, and a plurality of outer gas injection nozzles that are mounted in the burner end of the housing so as to direct gaseous fuel into the outer combustion zone. A first castellated ring is mounted around the periphery of the inner air tube, and a second castellated ring is mounted around the periphery of the burner end of the housing. The burner assembly also includes an igniter that is mounted in the burner end of the housing.
In a preferred embodiment, a liquid fuel system is provided in the burner end of the housing. In this preferred embodiment, an atomizing air tube is mounted within the housing. The atomizing air tube has an inlet end located downstream of the impeller and an outlet end located adjacent to the inner combustion zone. Also in this preferred embodiment, an atomizing nozzle is mounted on the outlet end of the atomizing air tube, a liquid fuel supply tube is mounted within the atomizing air tube so as to convey liquid fuel to the atomizing nozzle, a compressed air supply tube is mounted within the atomizing air tube so as to convey compressed air to the atomizing nozzle, and a third castellated ring is mounted around the periphery of the outlet end of the atomizing air tube.
In another preferred embodiment, a supplemental natural gas injection system is provided in the burner end of the housing. The supplemental natural gas injection system includes a premix natural gas nozzle, a natural gas manifold in fluid communication with the premix natural gas nozzle, a means for mixing combustion air and natural gas, and a plate mounted on the inner air tube. The plate includes a heat fin and an outer air castellated flame holder cup. In this preferred embodiment, a diverging conical discharge section is located downstream from the converging focusing cone and an adjustable opening band is mounted between the diverging conical discharge section and the converging focusing cone.
In order to facilitate an understanding of the invention, the preferred embodiments of the invention are illustrated in the drawings, and a detailed description thereof follows. It is not intended, however, that the invention be limited to the particular embodiments described or to use in connection with the apparatus illustrated herein. Various modifications and alternative embodiments such as would ordinarily occur to one skilled in the art to which the invention relates are also contemplated and included within the scope of the invention described and claimed herein.